Magnetism

Magnetism

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  Presented by : ArvindSingh Heer MSc-I (Sem-II) Inorganic Chemistry MITHIBAI COLLEGE MAGNETISM
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  CONTENT  INTRODUCTION  TYPESOF MAGNETISM  CURIE AND CURIE WEISS LAWS  MAGNECTIC SUSCEPTIBILITY
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  INTRODUCTION Magnetism is aproperty of materials that respond to an applied magnetic field that cause the material to be either attracted or repelled.
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  TYPES OF MAGNETISM Paramagnetic Ferromagnetic Antiferromagnetic ferrimagnetic
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  Diamagnetic  Feebly repelledby the magnetic fields. Non-metallic elements (excepts O2, S) inert gases and species with paired electrons are diamagnetic  All paired electrons  TiO2, V2O5,NaCl, C6H6(benzene)  Insulator
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  Paramagnetic  Attracted bythe magnetic field due to the presence of permanent magnetic dipoles (unpaired electrons). In magnetic field, these tend to orient themselves parallel to the direction of the field and thus, produce magnetism in the substances.  At least one unpaired electron  O2, Cu2+, Fe3+, TiO, Ti2O3, VO, VO2, CuO  Electronic appliances
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  Ferromagnetic  Permanent magnetismeven in the absence of magnetic field, Above a temperature called Curie temperature, there is no ferromagnetism.  Dipoles are aligned in the same direction  Fe, Ni, Co, CrO2  CrO2 is used in audio and video tapes
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  Antiferromagnetic  This ariseswhen the dipole alignment is zero due to equal and opposite alignment.  MnO, MnO2,Mn2O, FeO, Fe2O3; NiO, Cr2O3, CoO, Co3O4,
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  CURIE LAW This lawindicates that the susceptibility of paramagnetic materials is inversely proportional to their temperature, i.e. that materials become more magnetic at lower temperatures. The mathematical expression is: M- magnetisation X- magnetic susceptibility H- magnetic field T- absolute temperature C- curie’s constant
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  CURIE & WEISSLAW The temperature dependence of which requires an amended version of Curie's law, known as the Curie–Weiss law: θ - Weiss constant
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  MAGNETIC SUSCEPTIBILITY Magnetic susceptibilityis related to the force experienced by a substance in a magnetic field The magnetic moment is calculated from the magnetic susceptibility, since the magnetic moment is not measured directly The magnetic susceptibility per unit volume is K = I/H
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   Generally, itis more convenient to use mass units,therefore the mass or gram susceptibility is defined as: xg =k/d where d is the density of the solid.  The molar susceptibility is the mass susceptibility multiplied by the formula weight. xm= xg(F.W. in g mol ) -1
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   In theFaraday balance the field is inhomogeneous.  The pole pieces of the magnet are so shaped that there is region in which the product of the field strength and field gradient in the z direction is constant.  The sample is placed in this region.  The force in this case is independent of the packing of the sample and depends only on the total mass of the material present.  The method is sensitive and highly reproducible and can be applied to single crystals  The force is measured as a weight change, using a torsion balance.
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  Magnetic behavior maybe distinguished by the values of χ and μ and by their temperature and field dependence 1. Positive vs. negative value: only diamagnetic materials show negative χ 2. Absolute value: ferromagnetic materials show huge positivevalue 3. Temerature dependence: diamagnetism is not temp. dependence, antiferromagentic materials increase with increasing temp, and para- and ferromagnetic materials decrease with increasing temp
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  REFERENCE Chemical Structure andBonding H.B. Gray R.L. Dekock -THANK YOU